Table 2.

Level of precision: current and needed sample sizes.

Risk factor and round of data collection		Paper sample size, n	Precision with existing paper sample, proportionate terms	Digital sample size, n	Precision with existing digital sample, proportionate terms	Required sample size for estimation within 1 percentage point (0.01), n	Required sample size for estimation within 0.5 percentage points (0.005), n
Helmet use
	Winter	34,309	0.006	24,283	0.007	9595	38,377
	Summer	29,286	0.006	24,778	0.007	9585	38,338
Seatbelt Use
	Winter	36,573	0.006	25,452	0.007	9603	38,411
	Summer	35,434	0.006	27,423	0.006	9604	38,414
Speeding data
	Winter	30,634	0.004	24,799	0.006	7827	31,307
	Summer	30,190	0.004	25,783	0.006	8459	33,835